Heretofore, providing for cylinder locks or other locks for doors, it is necessary to carefully and correctly drill a cylindrical opening transversely through the door edge on a first axis and thereafter and successively carefully drill a further aperture into the door edge upon a second axis at right angles to the first axis and coplaner therewith, and wherein the second aperture is coincident with and registers with the first aperture in order to cooperatively receive the door lock assembly and lock cylinder, etc. Various means have been heretofore employed, essentially, a hand operated bit or bits for drilling the respective apertures. Some of the difficulties involved are making sure that the axes of the respective apertures are coincident and are at two right angles to each other. Further problems arise in drilling the door in such a way as not to splinter or otherwise damage the outer surfaces of the door style or rail, or to otherwise mar the door edges. Further problems exist in the careful locating and drilling of such apertures wherein door locks are provided for indoor and outdoor doors, and wherein the doors are of different thickness.